This article offers a discursive analysis of UK Parliamentary debate on the proscription of terrorist organisations between 2002 and 2014. It argues that these debates play an important constitutive role in the (re)production of national Self and terrorist Other that remains largely overlooked in existing work on this counter-terrorism mechanism. The article begins with an overview of this literature, arguing it is overwhelmingly oriented around questions of efficacy and ethics. While important, this focus has concentrated academic attention on the causal question of what proscription does, rather than the constitutive question of what is made possible by proscription. The article’s second section situates our analysis within discursive work in International Relations, upon which we investigate three pervasive themes in Parliamentary debate: (i) Constructions of terrorism and its threat; (ii) Constructions of specific groups being proscribed; and, (iii) Constructions of the UK Self. We argue that these debates (re)produce an antagonistic relationship between a liberal, open, and responsible UK mindful of cultural and religious difference, on the one hand. And, on the other, its illiberal, irrational terrorist Others conducting immoral violences on behalf of particularistic identity claims. This analysis, we conclude, has significance for contemporary debate on security politics, as well as for studies of counter-terrorism and international politics more generally.